Adjustable spring tension means



March 4, 1969 A. J. KRYSPIN 3,431,522

ADJUSTABLE SPRING TENSION MEANS Filed April 14, 1967 INVENTOR ATTORNEYS 35 United States Patent Office 3,431,522 Patented Mar. 4, 1969 3,431,522 ADJUSTABLE SPRING TENSION MEANS Alfred J. Kryspin, East Hanover, N.J., assignor to Automatic Switch Co., a corporation of New York Filed Apr. 14, 1967, Ser. No. 630,978 US. Cl. 335--194 4 Claims Int. Cl. H01h 3/22 ABSTRACT OF THE DISCLOSURE Two relatively movable parts, e.g., the core and armature of an electrical relay, are held in a predetermined relationship by a coil tension spring. One end of the spring is non-rotatably joined to one of the parts. The other end terminates in coils of smaller diameter than the remainder of the spring coils, and is threadably engaged by a screw carried by the other part. By turning the screw, the spring can be stretched or relaxed to vary its tension.

This invention relates to resilient tensioning means, and more particularly to means for adjusting the tension of a coil spring.

It is an object of the invention to provide an adjustable coil spring tensioning means which is considerably less expensive than comparable conventional arrangements, because the coils of the spring are employed as one of the adjustment components.

It is another object of the invention to provide such a means admirably adapted to furnish the required tension between the relatively movable parts of electrical devices, such as relays and solenoid-operated equipment, e.g. valves.

In brief, the invention includes a coil spring secured at one end to one of two relatively movable parts. The securement is such that .the spring is not permitted to rotate freely about its longitudinal axis. The other end of the spring terminates in a helical form, and is threadably engaged by a screw carried loosely by the other relatively movable part. Consequently, rotation of the screw causes the spring to stretch or relax, depending upon the direction of rotation, whereby the spring tension is varied.

Advantageously, the portion of the spring engaging the screw has a smaller diameter than the remainder of the spring, for reasons which are pointed out below in the detailed description of one embodiment of the invention.

In the drawings:

FIG. 1 is plan view of an electrical relay incorporating a spring means according to this invention;

FIG. 2 is a vertical cross-sectional view taken on line 22 of FIG. 1;

FIG. 3 is an end View of the relay; and

FIG. 4 is an exploded view of a spring and adjustment screw with which it is cooperable.

The device chosen to illustrate this invention is an electrical relay, including a base plate adapted to be mounted on some stationary support. The core of an electromagnet is mounted on the base plate by means of a screw 11, the core comprising an L-shaped member 12, and a post 13, both of magnetic material. Wound around the post 13 is a solenoid, or coil, 14, the ends 15 of which extend toward a terminal block 18 also mounted on the base plate 10 by means of a screw 19.

The terminal block 18 is, of course, formed of insulation material, and carries a total of six terminals or binding posts. The ends 15 of the solenoid 14 are electrically connected to the two lowermost terminals 20 (only one being visible in FIG. 2). The terminals 20 are adapted to be connected to a suitable electrical control circuit capable of energizing the solenoid when the relay is to be actuated.

Pivotally supported on the upper end of the vertical arm of L-shaped member 12 is an armature 21 of magnetic material. The armature has substantially an L shape, but its arms are arranged at an angle slightly greater than Mounted on the upper surface of the armature, by means of a screw 22 is a non-magnetic block 23 supporting a pair of spring biased, movable contact fingers 24, each of which carries a contact button 25. Arranged in the path of downward movement of the contacts 25 is a pair of fixed contacts 28 electrically connected to terminals 29 mounted in the terminal block 18. The third pair of terminals 30 are electrically connected to the rear ends of contact fingers 24 by wires 31.

When sufficient current is applied to the solenoid 14, the armature 21 will be attracted to the post 13, and hence the armature rotates in a clockwise direction in FIG. 2, to bring the movable contacts 25 into engagement with the fixed contacts 28. When the solenoid 14 is deenergized, the spring tension means of the present invention, described below, rotates the armature back to the position of FIG. 2 and the contacts 25 and 28 are disengaged. Thus, external circuits connected to the terminals 29 and 30 will be controlled by operation of the relay.

The armature 21 is provided with an integral, rigid tab 34, struck out of the vertical arm of the armature. The tab 34 extends from the pivot axis of the armature in a direction opposite to the direction of the horizontal arm of the armature. Directly below and spaced from the tab 34, the base plate 10 is formed with an integral rigid tab 3 5. A coil spring 36 is stretched between the tabs 34 and 35. The upper end of the spring is formed as a hook 37 which extends over the top of the tab 34 and is accommodated by notches in the side edges of the tab 34. This connection between spring and tab prevents any significant axial rotation of the spring, although some rotational play is permitted. The lower end of the spring terminates in a helical shape, and is connected to the tab 35 via an adjustment screw 38. The threaded shank of the screw 38 fits loosely through a hole 39 in the tab 35', and an enlarged head 40 on the screw limits its movement toward the tab 34.

A special feature of the invention is the formation of the spring 36 with an effective region 41 of relatively large diameter coils, and a connection region 42 of smaller diameter coils. The coils 42 and adjustment screw 38 are so chosen that the screw is threadably accommodated within the coils. Consequently, when the screw 38 is rotated the coil region 42 of spring 36 moves axially along the shank of the screw. Thus, when the screw 38 is rotated in one direction, the region 42 of the spring moves down the screw toward the tab 35, thereby stretching the effective region 41 of the spring and increasing the force on the armature 31 tending to keep it in the position shown in FIG. 2. As a result, the current level required in the solenoid to pivot the armature toward post 13 is increased. Rotation of the screw 38 in the opposite direction will have the opposite effect.

Several advantages accrue from the two diameter spring formation described above. As is known, for the same diameter wire, the larger the diameter of the coils of a spring, the lower the rate of increase in tension as the spring is stretched. Thus, it is desirable to employ relatively large coils so that fine adjustment of spring tension can be achieved; hence the coils 41 are relatively large. On the other hand, the cost of screws increase with their diameter. Therefore, by employing a connection region 41 of relatively small diameter coils, a cheaper adjustment screw can be employed.

More important, by making the internal diameter of the spring region 41 larger than the adjustment screw diameter, the screw can be accommodated within the coils 41 without touching them. Thus, a relatively long screw 38 can be used, to permit a wide range of tension variation, but regardless of the adjustment, the number of coils in the etfective region 41 of the spring remains the same. In contrast, if the spring 36 had a constant diameter throughout its length, each rotation of the adjustment screw tending to stretch the spring would withdraw another coil from the elfective, force-producing region of the spring.

Furthermore, stretching the spring obviously reduces the number of its coils per unit length, whereas the number of threads per unit length of the screw remains constant. Hence, if the spring had a constant diameter, a point would be reached, upon tensioning of the spring, at which the spring coils and the screw would not be threadably engageable. With the spring of the present invention, however, all the stretching of the spring takes place in the region 41, hence the screw 38 and spring region 42 remain threadably engageable throughout the range of spring adjustment.

It will be appreciated, therefore, that the present invention provides an adjustable spring tension means which is inexpensive to manufacture, assemble, and service, and which nevertheless offers a wide range of tension adjustment.

The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in the invention which will still be comprised within its spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended claims.

What is claimed is:

1. A device having first and second relatively movable parts, and adjustable spring tension means for movably maintaining said parts in a predetermined relationship, said means comprising a screw carried by said first part, said screw having a threaded portion and being freely rotatable and freely slidably in an axial direction with respect to said first part, means for limiting the axial movement of said screw toward said second part, and a coil spring non-rotatably joined to said second part, said spring having a region of relatively large diameter coils and a region of smaller diameter coils, all of said smaller coils being of the same diameter and at least some of said smaller diameter coils being located within the threads of said screw, whereby said smaller coils move longitudinally along the said screw as the latter is rotated so as to vary the tension in said larger coils, said screw being longer than the region of smaller diameter coils but the number of said larger diameter coils remaining the same regardless of the extent to which said screw is rotated to vary the tension in said larger coils.

2. A device as defined in claim 1 wherein said first part is provided with a hole through which said screw passes, the diameter of said hole being larger than the diameter of said screw, and said limiting means is a head on said screw having a dimension larger than the diameter of said hole so that said head will not pass through said hole.

3. A device as defined in claim 1 wherein one of said parts includes a solenoid, and the other of said parts includes an armature movable with respect to said solenoid and against the force of said spring when electric current is supplied to said solenoid.

4. A device as defined in claim 1 wherein said device is an electrical relay, said first part including a solenoid wound on a relatively stationary core, stationary contacts fixed with respect to said coil, said second part including an armature mounted for movement with respect to said core, and movable contacts carried by said second part adapted to engage said stationary contacts when said solenoid is energized and causes said armature to move against the force of said spring.

References Cited UNITED STATES PATENTS 1,098,956 6/1914 Miller 2671 1,327,951 1/1920 Haas 335-194 2,097,410 10/1937 Beiderman 335-197 2,932,704 4/ 1960 Dennison 335194 FOREIGN PATENTS 638,614 6/1950 Great Britain. 1,252,745 12/ 1960 France.

BERNARD A. GILHEANY, Primary Examiner.

D. M. MORGAN, Assistant Examiner.

US. Cl. X.R. 267l 

